1. Field of the Invention
This invention relates to a method for displaying an image on a display device having light-emitting elements with three primary colors (RGB) aligned with each other, and display equipment including the display device.
2. Description of the Related Art
Display equipment that employs various types of display devices have been in customary use. One known type of display equipment heretofore includes a display device such as a color LCD and a color plasma display, in which three light-emitting elements for illuminating three primary colors (RGB) are aligned in certain sequence to form a pixel. A plurality of pixels are aligned in series in a first direction, thereby forming a line. A plurality of lines are aligned in a second direction perpendicular to the first direction, thereby forming a display screen on the display device.
A large number of display devices have display screens reduced in size to a degree that they fail to provide a sufficiently fine display. This problem is commonly seen in the display devices disposed in, e.g., a cellular phone, a mobile computer. In such display devices, small characters and photographs, or complicated pictures, are often smeared and rendered obscure in sharpness.
In order to provide improved display sharpness in such a small display screen, a reference entitled “Sub-Pixel Font-Rendering Technology” is open to the public on the Internet. The reference discloses per sub-pixel display based on a pixel formed by three light-emitting elements (RGB). The present Inventors downloaded the reference on Jun. 19, 2000 from a web site (http://grc.com/) or a subordinate thereof.
The above technology is now described with reference to FIGS. 28 to 32. In the following description, an alphabetic character “A” is used as an example of a displayed image.
FIG. 28 is a simulated illustration, showing a line that includes a chain of pixels, each of which consists of the three light-emitting elements. A horizontal direction, or a direction in which the light-emitting elements are aligned with each other, is called a first direction. A vertical direction, perpendicular to the first direction, is referred to as a second direction.
In the prior art as well as the present invention, the light-emitting elements are not limited to alignment in the order of R, G, and B, but may be arranged serially in any other alphabetical sequence.
A plurality of the pixels, each of which is formed by the three light-emitting elements, is arranged in a row in the first direction to form a line. A plurality of such lines are aligned with each other in the second direction, thereby providing a display screen.
The sub-pixel technology as discussed above addresses an original image as illustrated in, e.g., FIG. 29. In this example, the character “A” is displayed over a display screen area that consists of seven pixels-by-seven pixels in the horizontal and vertical (first and second) directions, respectively. Meanwhile, a font having a resolution as much as three times greater than that of the previous character is provided as illustrated in FIG. 30 in order to provide a per sub-pixel display. In FIG. 30, assuming that each of the light-emitting elements (RGB) is viewed as a single pixel, the character “A” is displayed over a display screen area that consists of twenty-one pixels (=7*3 pixels) horizontally by seven pixels vertically.
As illustrated in FIG. 31, a color is determined for each of the pixels of FIG. 29, but not the pixels in FIG. 30. However, color irregularities occur when the determined colors are displayed without being processed. The determined colors must be filtered using factors as shown in FIG. 32(a) to avoid the color irregularities. As illustrated in FIG. 32(a), the factors are correlated with luminance, in which a central target sub-pixel is multiplied by, e.g., a factor of 3/9. Contiguously adjacent sub-pixels next to the central sub-pixel ae multiplied by a factor of 2/9. Sub-pixels next to the contiguously adjacent sub-pixels are multiplied by a factor of 1/9, thereby adjusting the luminance of each of the sub-pixels.
Apart from the above, anti-aliasing has been practiced in order to provide improved image visibility over a small display screen area. However, a drawback to anti-aliasing is that the entire image is rendered obscure in sharpness in order to alleviate jaggies, resulting in proportionally reduced image quality.
In view of such shortcomings, the use of the sub-pixel technology as discussed above provides better image visibility than anti-aliasing.